Method for coating cutting edges of sharpened instruments



Nov. 1, 1966 J. c. HOLMES ET AL 3,283,117

METHOD FOR COATING CUTTING EDGES OF SHARPENED INSTRUMENTS 2 SheetsSheet 1 Filed April 22, 1965 Nov. 1, 1966 J. c. HOLMES ETAL 3,283,117

METHOD FOR COATING CUTTING EDGES OF SHARPENED INSTRUMENTS Filed April 22, 1965 2 Sheets-Sheet 2 United States Patent 3,283,117 METHOD FOR COATING CUTTING EDGES OF SHARPENED INSTRUMENTS Joseph C. Holmes, Harrisonburg, Va., and George R.

Stepanelr, Akron, Ohio, assignors to Philip Morris Incorporated, New York, N.Y., a corporation of Virginia Filed Apr. 22, 1965, Ser. No. 449,941 Claims. (Cl. 219-76) This invention relates to a method for coating the cutting edges of sharpened instruments. "It is particularly concerned with a method for coating the finely honed edges of sharpened instruments suitable coating materials by means of an electrical plasma jet or a gas stream heated to the temperatures required by such other means as electrical resistance heating or combustion of proper gases.

The cutting edges of sharpened instruments such as knives, razor blades, shears, scissors, scalpels, surgical blades and the like are affected by certain deficiencies and limitations in their structure. For one thing, the material from which the instruments can be made is limited to those materials that can be conveniently shaped or rolled by conventional steel mill practice into stock forms suitable for handling by conventional grinding equipment since grinding is the most widely used means of forming and sharpening the edges. The grinding operation, how ever, generates heat which may change the properties of the edge material and also leaves minor surface imperfections in the edges. The latter are undesirable from the standpoint that they increase the cutting force which must be applied to the instrument in use. Furthermore, those materials which can be shaped or rolled by conventional steel mill practice into forms suitable for grinding are limited in their strength and, thereby, severely limit the edge shape and edge angles that can be generated thereon. In addition, since the physical and chemical properties of the cutting edge stock are the same as the severely limited physical and chemical properties of the substrate, severe limitations are placed on the resistance of the cutting edge to corrosion, deformation, dulling and like condi-tions which curtail the useful life of the cutting instrument or necessitate its rehoning if that is possible or practical.

The present invention has for its principal objects the provision of a method for coating the cutting edges of sharpened instruments with suitable materials soas to improve their cutting action while reducing the cutting force required. Another object is to provide for the reduction of corrosion in the cutting edges and for materially prolonging the useful life of the cutting edges.

Particular embodiments of the present invention are concerned with coating the cutting edges of razor blades with suitable materials. The latter may include both organic and inorganic materials which are capable of being thermally fused to the blade material by the application of the high intensity heat of an electrical plasma jet or other suitably heated gas source only to the locality of the cutting edges. According to the invention, the honed cutting edges of the razor blades may be first coated with a suitable material, as for example, Teflon. The Teflon coating and blade cutting edges are then exposed to an electrical plasma jet which heats the coating and cutting edges to a temperature sufficient to fuse the coating to the cutting edge material. Instead of precoating the cutting edges, the coating material may be applied to the cutting edges simultaneously with the exposure thereof to the electrical plasma jet. In the latter case, the coating material which is preferably in finely powdered form, although it may also be in rod form, is introduced into the electrical plasma jet gun in or near the plasma which "ice heats the material to or near fusion temperature while at the same time it feeds the material onto the cutting edges, where it becomes fused to the cutting edges.

The invention will appear more clearly from the following detailed description when taken in conjunction with the accompanying drawings showing by Way of example preferred embodiments of the inventive concept.

In the drawings:

FIGURE 1 is a schematic View in perspective illustrating the coating of a stack of razor blades with an electrical plasma jet gun wherein the blade cutting edges have been previously coated with a suitable material and the material thermally fused to the cutting edges by the action of the electrical plasma jet.

FIGURE 2 is a sectional view through a razor blade illustrating in magnified scale the coating applied to the cutting edge thereof.

FIGURE 3 is a schematic illustration of the apparatus used for coating the cutting edges of a continuous strip of sharpened razor blade stock wherein the coating material is first applied to the cutting edges and thereafter fused thereto by exposing the coating and the blade cutting edge to the plasma stream of an electrical plasma jet FIGURE 4 is a side elevation showing one positioning, relative to the cutting edge of the blade strip, of electrical plasma jet guns which may be used in the apparatus of FIGURE 3.

FIGURE 5 is an end elevation showing still other electrical plasma jet gun positionings which may be employed in practicing the present invention.

FIGURE 5a is a sectional view of a known type of electrical plasma jet gun nozzle which may be used for directing a plasma stream against both sides of razor blade strip.

FIGURE 6.is the same as FIGURE 3 except that the coating material is applied to and fused on the blade strip cutting edges in a single step.

FIGURE 7 is a vertical sectional view through one form of an electrical plasma jet gun which may be used in the apparatus of FIGURE 6 and illustrates in particular, the means for feeding the coating material in powdered form directly into the plasma stream.

FIGURE 8 is a vertical sectional View through a maximum dwell nozzle of known type which may be used in the electrical plasma jet gun of FIGURE 7.

FIGURE 9 is an end elevation showing the tip of the nozzle illustrated in FIGURE 8.

FIGURE 10 is a schematic plan view illustrating the manner in which a blade cutting edge coated in accordance with the present invention is subjected to a paper out test.

Throughout the specification, like reference numerals are used to indicate like parts.

Referring in detail to the drawings, there is illustrated in FIGURE 1 a stackof razor blades 10 which may be clamped together as shown by any known means. The blades 11 are, by Way of example, injector type razor blades on which a single cutting edge 12 has been ground and honed, although they also could be of the double edge type. The blades can be made from various materials including carbon steel, stainless steel, or high-strength plastic material. Eachblade 11 has a single cutting edge 12 formed by two intersecting or tapering sides as shown.-

According to the method employed in FIGURE 1, the blade cutting edges 12 are precoated with a suitable anti-friction material 13 in known manner as for example, by spray coating, the material being compatible with the blade material for thermal fusion thereto. The coating materials may include, but are not necessarily limited to, tungsten carbide, alloys, bimetals, metal oxide, polytetrafluoroethylene, polychlorotrifluoroethylene, fluorinated telomers, polyethylene, stearic acid, behenic acid, waxes, nylon, polymides, polyacetals and polycarbonates. It will be apparent that the method shown in FIGURE 1 is not limited to use in coating the cutting edges of razor blades but is equally suited for coating the cutting edges of any sharpened instrument. Furthermore, it is not necessary that the cutting instruments be stacked in a group for coating since they may also be coated individually or in continuous strip fashion, as in production line manufacturing.

Referring again to FIGURE 1, the coating material 13 covers the cutting edge of the blades but is not fused thereto until it is subjected to the high-intensity heat of an electronic plasma jet. For the latter purpose, an electrical plasma jet gun 14 of a type well known in the art is employed. In brief, the electrical plasma jet gun comprises a pair of electrodes between which is stuck an arc in the medium of a highly ionized inert gas such as argon, helium, nitrogen or hydrogen, or mixtures of these gases. The gun thus generates and sustains a plasma jet or stream 15 of highly-heated ionized gas which, according to the invention, is directed against the coated cutting edges of the blades. The plasma jet 15 is employed to apply concentrated heat to both the coating materials and the blade cutting edge to bring them to at least that temperature at which the coating material will fuse to the blade material. When fusing the coating on the blades as shown, the tip of the plasma jet gun (nozzlenot shown) is preferably maintained at a distance of approximately 1 /2"-4" from the blade cutting edges. In practice, of course, the plasma jet 15 envelops the cutting edge 12. It is not shown striking the cutting edges in FIGURE 1 only for purposes of illustrating other details therein.

As seen in FIGURE 1, the electrical plasma jet gun 14 is preferably maintained to direct the plasma jet against the cutting edge at an angle of 15 with the horizontal. Furthermore, the gun is moved relative to the cutting edge with longitudinal L-L and vertical V-V' movements as shown. In effecting these movements, the gun may be manipulated by hand or it may be mounted on a suitably powered fixture. It will be apparent that the last-mentioned movements of the gun 15 are employed for fusing the coating on only one side of the blade cutting edge and that the gun must be moved to the opposite side of the blade stack for fusing the coating on the other side of the cutting edge. Good simultaneous fusion of the coating material to both sides of the cutting edge may be achieved by positioning the electrical plasma jet gun 14 so that the plasma jet or stream 15' therefrom strikes the cutting edge at a 90 angle as shown. With this particular positioning, the gun 14' is simultaneously given a longitudinal motion L -L and transverse or lateral movement T-T'.

. An important advantage in using an electrical plasma jet gin for heating the cutting edges of the blades, is that.

heating is localized to the cutting edge only, so that the heat is rapidly carried therefrom by the rest of the blade body which acts as a cooling sink, thus inhibiting oxidation of the blade edge material.

FIGURE 2 illustrates a section through a blade 20, the cutting edge 21 of which has been coated with a fused coating 22 illustrated by way of example as being plastic although it may also be one of the inorganic materials hereinbefore described. The coating thickness has been exaggerated for purposes of clarity since in practice it only need be as thick as 0.001" or even less.

FIGURE 3 illustrates the method as employed for coating a continuous strip 30 of single edge razor blade stock. As shown, the continuous strip is sharpened with con ventional sharpening apparatus 35 to sharpen a cutting edge 31 von each blade segment 32. As used herein, sharpening includes rough grinding, finish grinding, honing and stropping operations. The strip thereafter is sprayed with a suitable solvent 33 by means of a suitable spray head 34 to remove ground metal and abrasive particles of the sharpening apparatus 35 from the cutting edges along with any residual honing coolant thereon. Thereafter, the blade strip passes under an air dryer unit 36 which dries and preheats the blades. The cutting edges of the strip are then coated with a coating material 37 such as Teflon powder (10 micron size) in suspension by means of a suitable spray device 38. The advancing strip thereafter passes under a second drying unit 39 which dries the coating material so that it forms a relatively thin solid layer over the cutting edges and the sides thereof. The coating is then fused to the cutting edge by means of one or more fixed electrical plasma jet guns 48', the plasma jets 41 of which are directed against only the cutting edge portions of the strip. The strip is thereafter advanced through a conventional blade breaker 42 which breaks the strip into individual blade units as shown.

To facilitate the use of the coating method illustrated in FIGURE 3, one or more electrical plasma jet guns 45, 46 may be positioned over the advancing strip as shown in FIGURE 4. The guns may be fixed one on each side of the blade strip and arranged so that the plasma jets 47, 48 therefrom are directed against the blade cutting edge at an angle of 30 to the horizontal and parallel to the plane of the blade strip. The gun positionings are not limited to that shown in FIGURE 4 but may also be those shown in FIGURE 5 wherein for example, a pair of guns 50, 51 are arranged one on either side of the blade strip 52 and their plasma jets 53, 54 directed against the cutting edge at an angle of 0. It is also possible to arrange the guns at an angle of 15 below the horizontal as shown in dashed lines.

FIGURE 5a illustrates still another gun arrangement for directing plasma against both sides of a blade simultaneously from one nozzle. The plasma jet gun 56 is positioned directly beneath a moving blade strip 57. The gun has a nozzle which is slotted as at 101 wherein travels the blade strip. The nozzle also has symmetrical slots 102, 103 from which issue respectively the plasma jets 58, 59, the latter being directed against the ground edges of the blade strip at an angle between 0-15 below the horizontal as shown.

The following examples describe the coating of a continuous strip of razor blade stock in accordance with the method illustrated in FIGURE 3.

Example I A continuous strip of steel, single edge razor blade stock was sharpened as shown in FIGURE 3 forming cutting edges on each blade segment of the strip. The cutting edges were then cleaned with a solvent and hot air direct-ed against the edges to dry and preheat them. An air spray gun then used to spray coat a Teflon (polytetrafluoroethylene) coating (dispersion of 2 /2% Teflon powder in water) on the cutting edges. The sprayed-on coating was then dried by passing the blade strip under a stream of heated air. The coating was then fused to the cutting edges by pasi-ng the strip under one or morefixed electrical jet plasma guns with the plasma jets therefrom contacting the coating and cutting edges. The guns used were AVCO plasma generators with an AVCO model 9013321 nozzle (anode) and model 901066-1 cathode. The guns were fixed at an angle of 15 to the blade cutting edges and the nozzle tip-to-blade edge distance was 3 /2 inches. Plasma gas flow to each gun was 1.85 s.c.f.m. 1 of argon. Plasma arc voltages was 28-30 volts with plasma arc current being 800 amperes. Strip speed moving past the plasma jet was 25 feet/min.

The coated blade was then broken from the strip. Upon examination, the Teflon coating showed good fusion and was generally smooth in appearance. The blade 1 Defined as the volumetric flow per minute of argon at 60 F. and atmospheric pressure.

Example II The procedure of Example I was repeated except that the following changes were made: strip speed was reduced to 12.5 feet/min; the plasma arc current reduced to 300 amperes; the nozzle tip moved to within 1% inches of the blade edges; the gun fixed at an angle of with the horizontal; and the plasma gas flow reduced to 1.38 s.c.f.m.

A coated blade broken from the strip was then examined. Fusion was excellent and the Teflon coating remarkably clear without any indications of cloudiness. The blade was then shave tested. A marked reduction in drag and shaving force required was noted.

According to the present invention, it is also possible to simultaneously apply and fuse the coating material to the cutting edge of a continuous strip of razor blade stock. As seen in FIGURE 6, the blade strip 60 is sharpened with a cutting edge 67 by means of sharpening apparatus 61, cleaned with a solvent and the solvent dried and the blade strip preheated as described before. The blade strip then passes under one or more electrical plasma jet guns 62, 63 into the plasma 64, 65 of which is fed in powdered form, the coating material 66, the latter being fed into the plasma jet guns by means of acarrier gas. The coating material is supplied from a suitable reservoir 68 which includes means such as a feed screw device (not shown) to accurately meter the powder flow and which is connected to the plasma jet guns by means of conduits 69. It is necessary that powder flow to the plasma jet guns be accurately controlled to give a uniform flow at a low feed rate, ttor example, grams per minute. Uniform powder flow is essential for achieving a coating of uniform thickness on the blade strip. In practice, a feed screw device with minimum land area was found to provide excellent results. The coating material is converted from a powdered to a fluid state immediately upon entering the plasma jets and is thereafter directed by the plasma jets against the cutting edges.

In the case of Teflon, the heat of the plasma jet causes a partial decomposition of the Teflon forming highly reactive free radicals which react with the blade edge material to form a chemical bond therebetween. Thus, the plasma jet serves the dual function of heating the coating material and the blade cutting edge to the temperature required for fusion between the coating material and blade material. The blade strip is thereafter broken into individual blade units as described before.

The following examples describe simultaneous application and fusion of coating materials to a continuous strip of razor blade stock.

Example III Cutting edges were sharpened on a continuous strip state fused to the cutting edges as soon as it contacted them. The following parameters applied:

Gas used (plasma and carrier) argon Gas flow (plasma) s.c.f.h.' Gas flow (carrier) 7.2 s.c.f.h.

Power to jet plasma gun 2O kw. Dwell time of Teflon powder in jet 0.0002 to 0.0005

plasma gun second. Plasma temperature 750-800 F. Strip speed 20 ft./min.

Defined as volumetric flow per hour of argon at 60 F. and atmospheric pressure.

A coated blade broken from the strip was then subjected to a standard shave test panel. Smooth cutting action and markedly improved shave characteristics were noted.

Example IV A continuous strip of steel, single edge razor blade stock was sharpened as shown in FIGURE 6 to form cutting edges on each blade segment of the strip. The cutting edge were then cleaned with a suitable solvent after which they were dried and preheated in the same manner as described in Example I. The strip advancing at a sepped of 20 feet/min. was then passed under a pair of electrical plasma jet guns arranged one on either side of the strip cutting edges. The guns were AVCO plasma generators with AVCO model IPS1060 nozzles (anodes) and AVCO model 90l0661 cathodes. Teflon powder was fed directly into the plasma of each gun at a controlled rate. Plasma gas (argon) fl-ow to the guns was 1.1 s.c.f.m. Carrier gas flow was 0.32 s.c.f.m. A-rc voltage was 25-28 v-olts with are current being 400 amperes. The jet plasma guns were set at 15 to the cutting edges and the nozzle tips fixed 2 inches from the blade edges. The softened Teflon was entrapped in the plasma jet and directed thereby against the blade cutting edges with the Teflon fusing to the cutting edges instantly upon striking same.

A blade was then broken from the strip and examined. The Teflon coating was clear, well adhered and of uniform thickness. It remained intact when the blade was subjected to a paper cut test in the same manner described in Example I.

FIGURE 7 illustrates one form of electrical plasma jet gun which may be utilized with the apparatus illustrated in FIGURE 6. The gun may be positioned relative to the blade strip in the same positionings shown in FIGURES 4 and 5, and is a well-known type. As seen in FIGURE 7, it includes rear and front housing portions 70, 71 respectively, a cathode 72 which may be made of tungsten and a nozzle 73 which serves as the anode. Plasma gas is fed to the cathode chamber 74 by means of a conduit '75 and the housing is provided with water cooling chambers '76 which are fed by mean of inlet and outlet conduits 77, 78 respectively. The coating material is fed in powdered form through a suitable conduit 79 into a passage 80 in the anode 73 wherefrom it is directed into the plasma 81.

FIGURE 8 shows a preferable form of the nozzle or anode which may be used in the plasma jet gun of FIGURE 7. The nozzle 90 is of a known type and is provided with a passage 91 which directs the powdered coating material into the plasma well before the mouth 92 of the nozzle. The latter feature provides for a maximum dwell (0.0002 to 0.0005 second) of the material in the plasma to insure adequate heating of the material before it leaves the gun. It also permits better plasma jet control and reduces the power input required for operation. This is particularly important for example in the case of Teflon powder wherein the Teflon must be heated to at least 750 F. to insure that it is melted to proper viscosity or fluidity to insure proper adhesion to the blade cutting edge. On the other hand, materials such as carbides will require higher temperatures to melt at least surface portions thereof to insure effecting a metallurgical bond between the coating material and instrument cutting edge. The plasma jet gun may be operated, of course, to provide these higher temperatures.

It will be apparent from the foregoing that the present invention offers a number of advantages over prior art methods for coating the cutting edges of sharpened instruments. It lends itself most readily for use in production line procedures as it is only necessary to use a few simple items of apparatus such as the electrical plasma jet gun, spray cleaners, etc. They are relatively inexpensive in cost, simple to operate and require little space. This is to be contrasted with the heavy equipment such as heating ovens used in the prior art which in addition to their expense and bulk are time consuming, difficult to control and involve undesirable additional handling of the sharpened instruments. The latter drawbacks are also prevalent in other prior art methods such as those involving the use of electrical resistance, induction heating or infrared techniques.

Another important advantage of the present invention is that it permits the use of coating materials heretofore believed too expensive for use on cutting instruments because of the difficulty of applying these materials to the substrate. With the present invention, it is also possible to use a wide range of substrate materials such as carbon steel, stainless steel and even a high-strength plastic.

The present invention also contemplates that a Wide range of ethylene, propylene and tetrafiuoroethylene monomers may be polymerized to anti-friction polymers within the electrical plasma jet gun before spraying the same on the cutting edges as shown in FIGURE 6.

While there is disclosed but some embodiments of the coating method of the present invention, it is possible to produce still other embodiments without departing from the scope of the inventive. concept herein disclosed.

What is claimed is:

1. In the manufacture of cutting instruments in a continuous operation, a method for coating the sharpened cutting edges of the cutting instruments with a coating material to improve the cutting characteristics thereof comprising applying the coating material to the cutting edges while controlledly advancing the cutting instruments adjacent a stream of highly heated gas with said stream in contact with said coating material and cutting edges only, said stream of heated gas being adapted to heat said coating material and cutting edges to a temperature sufiicient to cause said coating material to bond to said cutting edges.

2. The method of claim 1 wherein the coating material is an inorganic material.

3. The method of claim 1 wherein the coating material is an organic material.

4. The method of claim 1 wherein the stream of highly heated gas is the plasma jet of an electrical plasma jet gun.

5. In a method for continuously manufacturing razor blades wherein cutting edges are sharpened on each of the blade segments of a continuous strip of razor blade stock, the steps of applying a coating material comprising an anti-friction material on said cutting edges while controlledly advancing said continuous strip adjacent at least one electrical plasma jet gun with the plasma jet thereof in contact With said coating material and cutting edges only, said plasma jet heating said coating material and said cutting edges to a temperature suflicient to cause said coating material to bond to said cutting edges.

6. The method set forth in claim 5 wherein the coating material comprises a liquid dispersion of powdered polytetrafluoroethylene, and is applied to the cutting edges before they are advanced into contact with said plasma jet.

7. The method set forth in claim 5 wherein said coating material is polytetrafluoroethylene and is applied to the cutting edges by entraining it in the plasma jet.

8. The method set forth in claim 5 wherein the coating material is applied to said cutting edges as a thickness of not greater than 0.001 inch.

9. The method set forth in claim 5 wherein the tip of the electrical plasma jet gun is positioned at a distance between about 1 /2 inches and 4 inches from said cutting edges, and said continuous strip is advanced adjacent said electrical plasma jet gun at a speed between about 12 /2 feet per minute and 25 feet per minute.

10. The method set forth in claim 5 further comprising providing the electrical plasma jet gun with a nozzle having a vertically slotted portion through which the continuous strip advances, and directing plasma jets from symmetrically opposed locations in said slotted portion against the cutting edges on said continuous strip at an angle of between 0 to 15 below the horizontal.

References Cited by the Examiner UNITED STATES PATENTS 1,791,968 2/1931 Morgan 219-77 2,806,124 9/1957 Gage 219-421 3,075,066 1/1963 Yenni et a1. 219-76 3,114,826 12/1963 Sullivan et al 219--76 3,179,784 4/1965 Johnson 219-76 RICHARD M. WOOD, Primary Examiner. 

1. IN THE MANUFACTURE OF CUTTING INSTRUMENTS IN A CONTINUOUS OPERATION, A METHOD FOR COATING THE SHARPENED CUTTING EDGES OF THE CUTTING INSTRUMENTS WITH A COATING MATERIAL TO IMPROVE THE CUTTING CHARACTERISTICS THEREOF COMPRISING APPLYING THE COATING MATERIAL TO THE CUTTING EDGES WHILE CONTROLLABLY ADVANCING THE CUTTING INSTRUMENTS ADJACENT A STREAM OF HIGHLY HEATED GAS WITH SAID STREAM IN CONTACT WITH SAID COATING MATERIAL AND CUTTING EDGES ONLY, SAID STREAM OF HEATED GAS BEING ADAPTED TO HEAT SAID COATING MATERIAL AND CUTTING EDGES TO A TEMPERATURE SUFFICIENT TO CAUSE SAID COATING MATERIAL TO BOND TO SAID CUTTING EDGES. 